The most prevalent proteins in the human lens are the crystallins. One of the major groups of these proteins are called gamma crystallins. Because of alterations in these crystallins upon aging in the lens and the difficulty in getting purified polypeptide, the protein sequences of these crystallins are not known. The nucleotide sequences of the gamma-crystallin family are known, however. As an alternate approach for assigning these genes to specific polypeptides, the genes for three of the gamma- crystallins were stably integrated into mouse L-cells, a fibroblast cell line. The products of these genes that were expressed in the fibroblasts could then be compared to the proteins found in the human lens. Three of the human gamma crystallins expressed in the mouse cells have been shown to have properties identical to the gamma-crystallins found in the human lens. The aging of crystallins in vivo has been difficult to study because the exact mechanism for the alterations is not known. By using the gamma-crystallins expressed in vitro in a mixed-function oxidation system, the microheterogeneity and shift to more acidic crystallin components found in the aging lens has been duplicated in vitro. In addition to the work on the gamma-crystallins, studies with lens membrane have also been done. A major protein in the membrane fraction of cell lenses has been identified as calpactin I. This protein is known to associate with actin in the presence of calcium and phospholipid. This protein may play a major role in the process of differentiation of lens epithelium to lens fiber.